The invention relates to clamps for welding, glueing, etc. in particular, but has application to wrenches, vises and other workholding equipment as well. In the use of welding clamps holding a multitude of metal pieces together in the position desired for permanent attachment by welding, it is often necessary to hold such pieces together against the force of gravity, and as the clamp is tightened, the spring of the pieces and the rotation of the screw will create forces to change their relative positions. The clamps used are variations of C-clamps in which a moveable jaw is forced towards a fixed jaw by a screw jack turned by hand. In such an operation, one hand is needed to hold the body of the clamp, one hand for turning the screw, and a third hand is needed to hold the work in place.
Improvisations using a knee, a jury rig lever temporarily welded to the work or work table, etc. are not only inadequate to take the place of the third hand, but are sometimes hazardous, time-consuming and poor substitutes for the third hand for holding the work in place. Thus there is a need for a one-hand operated welding clamp leaving the welder's other hand free to position the work and hold it in place until held in place firmly by the clamp.
A one-hand operated C-clamp is shown in Gilbert U.S. Pat. No. 2,472,658 having a rack-held moveable jaw which is dropped down against the work by gravity, and a lever and cam-operated pawl which is then engaged with the rack by a hand-squeeze handle to increase clamping pressure, locking it in that position in one stroke of the hand-squeeze handle. If the clamping movement is insufficient to properly clamp the work, a screw jack in the jaw head is rotated to adjust the jaw so that proper holding pressure is obtained. Since proper holding or clamping pressure may not always be obtained without use of the screw jack, on hand is needed to hold the clamp, a second to hold the work, and a third to operate the screw jack.
Cartridge dispensing caulking guns of conventional contemporary design such as Darworth Company of Avon, Connecticut Form No. CP-SS-276 use a hand-squeeze lever operated pawl and ratchet to advance the caulking gun piston with a second pawl engaging the ratchet teeth on the piston shaft to hold the piston between power strokes. The piston is released by the operator's other hand rotating the piston shaft thus lifting both pawls out of engagement with the ratchet teeth which are on only one side of the shaft. While such a mechanism has application to clamps, etc., it is limited because of its ratchet action with only fixed increments of closing motion and need for two hand operation for quick closing and release.
U.S. Pat. Nos. 2,967,445 (Chase) and 2,985,048 (DeHart) show vises in which a screw jack can be operated by a foot pedal. U.S. Pat. Nos. 1,460,294 (Wegner) and 2,321,911 (Heaton) show wrenches in which the last stage of closing or clamping is accomplished by lever action.